Bonded-fiber fabric for producing clean-room protective clothing

ABSTRACT

A nonwoven fabric for manufacturing repeatedly re-usable clean-room protective clothing, made of super microfilaments having a titer of less the 0.2 dtex that are produced by water jet splitting multicomponent multisegment filaments having a titer of less than 2 dtex, the primary filaments being spun from the melt, aerodynamically stretched, laid to form a nonwoven fabric, and subjected to water-jet prebonding prior to splitting.

DESCRIPTION OF THE TECHNICAL FIELD

Protective clothing for clean rooms has the function of protecting theproducts produced or processed in these rooms (e.g. microelectronicparts, pharmaceuticals, optical glass fibers) from people as the“source” of the emission of interfering particles (e.g. dust particlesor skin particles, bacteria).

Therefore, the most important requirement of the material formanufacturing such protective clothing is the barrier effect. Theprotective-clothing material must hold in particles constantly releasedby the human body (skin particles, hair fragments, bacteria, etc.) aswell as fiber fragments detached from a textile garment worn underneathin order to prevent the clean-room air and, thus, the product from beingcontaminated. Naturally, the material itself may also not release anyfiber fragments or other components into the clean-room air.

In addition to the necessary barrier effect, the protective-clothingmaterial must have a high mechanical load-bearing capacity, inparticular a high level of resistance to further tearing and abrasions,to minimize the danger of the formation of tears or holes due to outsideinfluences and/or the demands of normal wear. To be able to repeatedlyre-use the protective clothing, the material must also be able toundergo washing and cleaning processes customary in the field (e.g.sterilization in an autoclave) with as little damage as possible, i.e.,it must be resistant to wet-mechanical wear and pilling and besufficiently dimensionally stable.

In addition to the barrier effect and (wet) mechanical resistance, theprotective-clothing material, in particular for use in clean rooms ofthe microelectronics industry, must have an anti-static effect, i.e.,the material should not become excessively electrostatic as a result ofthe unavoidable friction when worn or should be able to quicklydissipate or discharge such charges. This is necessary, on the one hand,so that sensitive microelectronics components are not damaged bypoint-to-point discharging, and, on the other hand, so that dustparticles that could accumulate on the material's surface andpotentially be later re-emitted are not pulled in from the ambient air.

In addition, the protective-clothing material should also have asufficiently high level of wearability, i.e., have a character that isas textile-like as possible with respect to drape, feel, and appearanceand should be able to breathe and, if applicable, also beheat-insulating in order to prevent the wearer from sweating or freezingexcessively.

BACKGROUND INFORMATION

It is known to use synthetic fibers or synthetic filaments having anultra fine titer to manufacture clean-room protective clothing material.In this context, “ultra fine-titered” refers to fibers having a titer ofless than 1 dtex, which are also referred to a “microfibers.” The term“super microfibers” may also be used for microfibers having a titer ofless than 0.3 dtex.

Typical protective-clothing material on the basis of microfiber ormicrofilament woven fabrics or microfiber or microfilament knittedfabrics is produced in a plurality of method steps. Microfibers ormicrofilaments are first spun from raw polymer materials. These are thenfurther processed to form yarns, which undergo a subsequent texturingprocess if necessary. Finally, the actual protective-clothing materialis woven from the (textured) microfiber yarns or microfilament yarns. Inthe web process, conductive yarns are also able to be woven in the formof a regular pattern, e.g. in stripes or checks, to achieve the requiredanti-static effect. The conductive yarns contain, for example, core/coatfilaments having a soot-containing or graphite-containing core or coator also metal fibers or metalloid filaments, for example. The necessarybarrier function and the high (wet) mechanical load-bearing capacity areachieved by an extremely densely and regularly weaving the microfiberyarns. However, this high web density and the predominantlysurface-parallel filament orientation are unfavorable with respect tothe material's breath ability. There are only a few micro pores or microchannels through or via which water vapor can be transported through thewoven fabric.

The problematic property combination of barrier effect and breathability of the protective-clothing material may be achieved by usingparticle-tight, yet water-vapor permeable, membranes. Such “microporous” layers may be applied to textile materials of normal density,e.g. By lamination or direct extrusion, to obtain a material having atextile character.

The manufacturing method for high-density, microfilament woven fabricsas well as for composite materials of a breathable barrier membrane anda textile entails multiple steps and is, thus, relatively timeconsuming. Microfiber nonwoven fabrics present an easily manufacturedalternative.

Planar calendered microfilament spun bonded materials on a polyethylenebasis are able to satisfy the barrier requirements and are alsoparticularly inexpensive to manufacture. However, such materials arepractically air-tight and/or water vapor-tight and have a film-likecharacter, i.e., the wearability is minimal. Moreover, they are onlyinsufficiently wash fast or durable during cleaning, so that their useis limited to one-way or throw-away protective clothing.

Microfiber nonwoven fabrics made from multisegment or multi core staplefibers, which are split up into individual microfibers after the webformation and a possible prebonding via a solvent or water jets, shouldprovide significantly better wearability with a good barrier effect thanthe abovementioned high-calendered microfilament spun bonded materials.

European Patent 0 624 676 describes, for example, a method for usingwater jet splitting to manufacture a microfiber nonwoven fabric havingan extremely high bulk density and, consequently, also a good barriereffect. However, this nonwoven fabric lacks softness and heat insulationproperties. As a result, the use of water jet-bonded nonwoven fabricsfor the (protective) clothing industry is considered to be limited.Therefore, another method that does not use the water jet technique isproposed in the indicated patent.

Deviating from the abovementioned patent, PCT Application WO 98 1 23 804proposes first thermally heat sealing the nonwoven fabric in a pointwise manner, prior to the water jet splitting. This is intended toprevent the nonwoven fabric from interlocking with the sieve band of thewater-jet aggregate during the water jet splitting and from then beingdamaged or even destroyed when lifted. In addition, a higher degree offiber distribution is to be achieved, thereby resulting in improvedbarrier and touch properties.

European Patent 97 108 364 also strives to expand the scope ofapplication of nonwoven fabrics. The patent describes the manufacture ofa nonwoven fabric from very fine filaments, the nonwoven fabric beingintended to have properties similar to woven or knitted textiles. Thevery fine filaments having a titer of 0.005 to 2 dtex are produced viawater jet splitting from melt-spun, crimped, or non-crimpedmulticomponent, multisegment filaments having tinters from 0.3 dtex to10 dtex. The thus-produced nonwoven fabric can then be after treated indifferent ways (e.g. Via thermofixing, point calendering, etc.) toattain special working properties. The spun bonded materials producedaccording to this method are supposed to be particularly suitable formanufacturing articles of clothing and other textile products.

SUMMARY OF THE INVENTION

In subsequent tests, it was surprisingly determined that nonwovenfabrics produced according to abovementioned European Patent 97 108 364are particularly suitable for manufacturing clean-room protectiveclothing when they are made of super microfilaments having tinters lessthan 0.2 dtex and are also emboss-calendered. The super microfilamentsthemselves are produced by water jet splitting multicomponent filamentshaving a titer of less than 2 dtex that were formed using the meltspinning method, aerodynamically stretched, and prebonded using waterjets.

Therefore, the present invention describes a new nonwoven material aswell as the method steps for producing it. The nonwoven fabric satisfiesall requirements for a repeatedly re-usable clean-roomprotective-clothing material. It is distinguished by a high barriereffect, a high mechanical load-bearing capacity, high dimensionalstability, an efficient anti-static effect, as well as a high level ofwearability (breath ability and textile character). These favorableproperties are retained to a sufficient extent even after multiple,customary wash or cleaning processes (up to 30 cycles). Until now, thesum of these properties was considered to be impossible for a nonwovenfabric having split super-fine filaments.

The nonwoven fabric is made of super microfilaments having tinters ofless than 0.2 dtex that are produced from non-crimped primary filamentshaving a titer of 1.5 to 2 dtex. Bicomponent multisegment filaments oftwo incompatible polymers, in particular polyester and polyamide, arepreferably used as the primary filaments. This combination is known, andin this respect, reference is made to EP 97 108 364. The proportion ofpolyester is selected to be greater than that of polyamide, preferablybetween 60 and 70% by weight. To achieve the necessary anti-staticeffect, one of the two or both polymers are provided with suitableadditives that are permanently effective, i.e., not able to be washedoff or out. The anti-static effect can be achieved, e.g. By mixing insoot or graphite or by admixing polymers having a strong hydrophiliccharacter or polymers having (semi) conductive properties, whilepossibly adding compatibility agents. The primary bicomponent filamentshave a cross-section with an orange-like multisegment structure (piestructure). Each segment alternately includes one of the incompatible,additive polymers. This filament cross-section known per se has provento be favorable for the subsequently described production of the supermicrofilaments. Following the customary aerodynamic stretching, theprimary filaments undergo a further stretching and, at the same time,tempering process (hot-channel stretching) in order to achieve thedesired high scuff resistance and low pilling tendency of the nonwovenfabric

The thus-produced primary filaments are laid down in irregular order viaspecial aggregates onto a moving band and are subsequently prebonded,i.e., are mechanically intertwined with one another, using aconventional water jet technique. High-pressure water jets are thenapplied several times to both sides of the prebonded primary filamentnonwoven fabric on perforated drums, the primary filaments practicallycompletely disintegrating into their components, i.e., into theindividual super microfilaments, which are simultaneously intermingledwith one another in an extremely homogenous manner. This method stepproduces a microfiber nonwoven fabric that possesses the necessary highbarrier effect as a result of its extremely irregular and intermingledfiber structure, yet is also sufficiently permeable for water vapor.

To improve the dimensional stability during washing and cleaningprocesses, the microfiber nonwoven fabric undergoes a hot-airthermofixation process under tension after the water jet splitting andsubsequent drying. The nonwoven fabric is then emboss-calendered in acalender having a special embossing cylinder to further increase thedimensional stability and scuff resistance. The finished nonwoven fabrichas a mass per unit area of 80 to 150 g/m², preferably 95 to 115 g/m².

EXAMPLE

A nonwoven fabric is first produced having a mass per unit area of 95g/m² with a uniform thickness of bicomponent filaments consisting of 70%poly(ethylene terephthalate) and 30% poly(hexamethylene dipamide). Theprimary filaments have a titer of 1.6 dtex and contain 16 segments thatare alternately made up of the polyester and polyamide. The melt-spunfilaments are aerodynamically stretched, irregularly laid down on aband, and subjected to a water jet treatment in which the filaments arefirst prebonded. The prebonded nonwoven fabric is then treated usinghigh-pressure water jets, the primary filaments being split intoindividual segments and the individual segments being further coiled[twisted]. The water-jet splitting is carried out several times fromboth sides of the nonwoven fabric. The resulting super microfilamentshave an average titer of 0.1 dtex and are non-crimped. The nonwovenfabric is subsequently dried and emboss-calendered. The thus-producednonwoven fabric has a filter efficiency of about 60% for particles >0.5μm or of about 98% for particles >1 μm. After being washed 30 timesusing a standard detergent at 40° C., the filter efficiency decreasesonly insignificantly to about 55% for particles >0.5 μm or to about 95%for particles >1 μm.

What is claimed is:
 1. A nonwoven fabric for manufacturing repeatedlyreusable clean-room protective clothing, made of super microfilamentshaving a titer of less than 0.2 dtex that are in turn produced by waterjet splitting multicomponent filaments (referred to as “primaryfilaments” in the following) having a titer of less than 2 dtex, theprimary filaments being spun from a melt, aerodynamically stretched,directly laid to form a nonwoven fabric, and subjected to water-jetprebonding prior to splitting wherein the primary filaments representbicomponent filaments made of two incompatible polymers, in particular apolyester and a polyamide and at least one of the polymers has ananti-static additive prior to the primary filament being spun.
 2. Thenonwoven fabric as recited in claim 1, wherein the primary filamentsundergo an additional stretching and tempering process after theaerodynamic stretching.
 3. The nonwoven fabric as recited in claim 1,wherein the polyester proportion is greater than the polyamideproportion.
 4. The nonwoven fabrics as recited in claim 3, wherein thepolyester proportion is between 60 and 70% by weight with respect to thetotal weight of the nonwoven fabric.
 5. The nonwoven fabric as recitedin claim 1, wherein the polyester proportion is between 60 and 70% byweight with respect to the total weight of the nonwoven fabric.
 6. Thenonwoven fabric as recited in claim 1, wherein the mass per unit area ofthe nonwoven fabric is between 80 and 150 g/m².
 7. The nonwoven fabricas recited in claim 1, wherein the mass per unit area of the nonwovenfabric is between 95 and 115 g/m².
 8. The nonwoven fabric as recited inclaim 2, wherein the mass per unit area of the nonwoven fabric isbetween 80 and 150 g/m².
 9. The nonwoven fabric as recited in claim 1,wherein the primary filaments have a cross section having an orange-likemultisegment structure, the segments alternately containing one of thetwo incompatible polymers, respectively.
 10. The nonwoven fabric asrecited in claim 1, wherein the primary filaments are water-jet split byhigh-pressure water jets being alternately applied several times to bothsides of the prebonded nonwoven fabric.
 11. The nonwoven fabric asrecited in claim 10, wherein the water jet splitting is carried out onan aggregate having rotating, perforated drums.
 12. The nonwoven fabricas recited in claim 1, wherein the nonwoven fabric is emboss-calendaredafter being water jet split and subsequently dried.
 13. The nonwovenfabric as recited in claim 1, wherein the nonwoven fabric undergoes athermofixation and subsequent thermosetting after jet splitting.
 14. Thenonwoven fabric as recited in claim 1, wherein at least one twoincompatible polymers contains a permanently anti-statically acting sootor graphite additive, a poly(amide-block-ether) copolymer having apronounced hydrophilic character or a polyanaline or polyacetylenederivative polymer having (semi) conductive properties.
 15. The nonwovenfabric as recited in claim 1, wherein the super microfilaments arenon-crimped.